Treasury Secretary Jack Lew on Friday strongly defended the sanctions the U.S. has imposed on Russia and says the administration "sees many signs" that the sanctions are having an impact, including a downgrade of Russian debt.

"If you look at the conditions since we started imposing sanctions, they're having an impact," Lew told Marketplace in an interview. "Even the Russians are admitting that they are having an impact."

Lew added that the U.S. is working with its allies in Europe on another possible round of sanctions.

"We are working with our international partners to make sure that when we do it, we do it in an effective way," he said.

Lew said the goal of the sanctions is to damage the Russian economy while doing the least amount of damage to the rest of the global economy.

"When you stop doing business with a country as large as Russia, there are effects outside the boundaries of the country," Lew said. "There are American companies that are already feeling some of the pinch and there are European businesses that are feeling some of the pinch. And that's the goal: The goal is to affect the Russian economy."

Lew also talked about the slowdown of the economy in China, but said the slowdown itself shouldn't stop Beijing from reforming its economy.

"I have a sense that [in] the short term they will be able to manage through," Lew said. "I'm more concerned that they stay on the reform path because in the longer term, if they don't, the efficiency of their economy will suffer. And it will create more tension in the world."

Lew added that in conversations with China's leaders, "they don't disagree with us on what they need to do," it's a disagreement over the pace of change.

Lew spoke to Marketplace from Detroit, where he toured Detroit's Marygrove community Thursday, observing a government program to remove blighted and abandoned Detroit homes.

"It is a real problem when you have vacant houses that are stripped and the windows are broken," Lew said. "Everyone knows what happens on the street corner if a hubcap is taken off of a car. Pretty soon, the rest of the hubcaps are gone and the car is destroyed. That happens to neighborhoods also."

He said the broader U.S. economy is recovering, but housing and construction are still "slower than other parts of the economy" in coming back.

"Families don't forget quickly if they lost their home or lost their job," Lew said. "I view it as an opportunity – there is going to be pent-up demand that needs to be met."

Finally, when Lew's predecessor appeared on Marketplace, Timothy Geithner talked about changing his signature because "on the dollar bill I had to write something where people could read my name. That’s the rationale."

And Secretary Lew also famously tweaked his signature for the dollar bill.

"I've been working on my handwriting for over 50 years," he said in today's interview.